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I'm in the business
of safeguarding secrets,
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and this includes your secrets.
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Cryptographers are
the first line of defense
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in an ongoing war that's been
raging for centuries,
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a war between code makers
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and code breakers.
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And this is a war on information.
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The modern battlefield
for information is digital.
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And it wages across your phones,
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your computers
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and the internet.
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Our job is to create systems that scramble
your emails and credit card numbers,
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your phone calls and text messages --
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and that includes those saucy selfies --
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(Laughter)
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so that all of this information
can only be descrambled
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by the recipient that it's intended for.
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Now, until very recently,
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we thought we'd won this war for good.
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Right now, each of your smartphones
is using encryption
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that we thought was unbreakable
and that was going to remain that way.
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We were wrong,
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because quantum computers are coming,
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and they're going to change
the game completely.
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Throughout history,
cryptography and code-breaking
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has always been this game
of cat and mouse.
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Back in the 1500s,
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Queen Mary of the Scots thought
she was sending encrypted letters
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that only her soldiers could decipher.
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But Queen Elizabeth of England,
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she had code breakers
that were all over it.
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They decrypted Mary's letters,
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saw that she was attempting
to assassinate Elizabeth,
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and subsequently,
they chopped Mary's head off.
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A few centuries later, in World War II,
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the Nazis communicated
using the Engima code,
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a much more complicated encryption scheme
that they thought was unbreakable.
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But then good old Alan Turing,
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the same guy who invented
what we now call the modern computer,
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he built a machine and used it
to break Enigma.
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He deciphered the German messages
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and helped to bring Hitler
and his Third Reich to a halt.
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And so the story has gone
throughout the centuries.
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Cryptographers improve their encryption,
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and then code breakers fight back
and they find a way to break it.
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This war's gone back and forth,
and it's been pretty neck and neck.
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That was until the 1970s,
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when some cryptographers
made a huge breakthrough.
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They discovered an extremely
powerful way to do encryption,
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called "public-key cryptography."
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Unlike all of the prior methods used
throughout history, it doesn't require
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that the two parties that want to send
each other confidential information
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have exchanged the secret key beforehand.
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The magic of public-key cryptography
is that it allows us to connect securely
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with anyone in the world,
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whether we've exchanged
data before or not,
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and to do it so fast that you and I
don't even realize it's happening.
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Whether you're texting your mate
to catch up for a beer,
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or you're a bank that's transferring
billions of dollars to another bank,
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modern encryption enables us
to send data that can be secured
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in a matter of milliseconds.
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The brilliant idea that makes
this magic possible,
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it relies on hard mathematical problems.
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Cryptographers are deeply interested
in things that calculators can't do.
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For example, calculators can multiply
any two numbers you like,
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no matter how big the size.
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But going back the other way --
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starting with the product and then asking,
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"Which two numbers multiply
to give this one?" --
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that's actually a really hard problem.
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If I asked you to find which two-digit
numbers multiply to give 851,
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even with a calculator,
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most people in this room would have
a hard time finding the answer
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by the time I'm finished with this talk.
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And if I make the numbers a little larger,
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then there's no calculator on Earth
that can do this.
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In fact, even the world's
fastest supercomputer
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would take longer
than the life age of the universe
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to find the two numbers
that multiply to give this one.
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And this problem,
called "integer factorization,"
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is exactly what each of your smartphones
and laptops is using right now
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to keep your data secure.
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This is the basis of modern encryption.
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And the fact that all the computing power
on the planet combined can't solve it,
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that's the reason we cryptographers
thought we'd found a way
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to stay ahead of the code
breakers for good.
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Perhaps we got a little cocky,
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because just when we thought
the war was won,
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a bunch of 20th-century physicists
came to the party,
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and they revealed
that the laws of the universe,
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the same laws that modern
cryptography was built upon,
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they aren't as we thought they were.
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We thought that one object couldn't be
in two places at the same time.
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It's not the case.
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We thought nothing can possibly spin
clockwise and anticlockwise
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simultaneously.
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But that's incorrect.
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And we thought that two objects
on opposite sides of the universe,
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light years away from each other,
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they can't possible influence
one another instantaneously.
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We were wrong again.
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And isn't that always the way
life seems to go?
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Just when you think you've got
everything covered, your ducks in a row,
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a bunch of physicists come along
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and reveal that the fundamental laws
of the universe are completely different
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to what you thought?
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(Laughter)
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And it screws everything up.
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See, in the teeny tiny subatomic realm,
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at the level of electrons and protons,
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the classical laws of physics,
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the ones that we all know and love,
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they go out the window.
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And it's here that the laws
of quantum mechanics kick in.
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In quantum mechanics,
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an electron can be spinning clockwise
and anticlockwise at the same time,
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and a proton can be in two places at once.
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It sounds like science fiction,
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but that's only because
the crazy quantum nature of our universe,
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it hides itself from us.
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And it stayed hidden from us
until the 20th century.
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But now that we've seen it,
the whole world is in an arms race
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to try to build a quantum computer --
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a computer that can harness the power
of this weird and wacky quantum behavior.
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These things are so revolutionary
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and so powerful
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that they'll make today's
fastest supercomputer
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look useless in comparison.
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In fact, for certain problems
that are of great interest to us,
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today's fastest supercomputer
is closer to an abacus
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than to a quantum computer.
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That's right, I'm talking about
those little wooden things with the beads.
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Quantum computers can simulate
chemical and biological processes
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that are far beyond the reach
of our classical computers.
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And as such, they promise to help us solve
some of our planet's biggest problems.
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They're going to help us
combat global hunger;
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to tackle climate change;
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to find cures for diseases and pandemics
for which we've so far been unsuccessful;
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to create superhuman
artificial intelligence;
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and perhaps even more important
than all of those things,
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they're going to help us understand
the very nature of our universe.
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But with this incredible potential
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comes an incredible risk.
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Remember those big numbers
I talked about earlier?
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I'm not talking about 851.
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In fact, if anyone in here
has been distracted
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trying to find those factors,
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I'm going to put you out of your misery
and tell you that it's 23 times 37.
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(Laughter)
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I'm talking about the much
bigger number that followed it.
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While today's fastest supercomputer
couldn't find those factors
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in the life age of the universe,
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a quantum computer
could easily factorize numbers
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way, way bigger than that one.
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Quantum computers will break
all of the encryption currently used
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to protect you and I from hackers.
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And they'll do it easily.
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Let me put it this way:
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if quantum computing was a spear,
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then modern encryption,
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the same unbreakable system
that's protected us for decades,
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it would be like a shield
made of tissue paper.
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Anyone with access to a quantum computer
will have the master key
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to unlock anything they like
in our digital world.
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They could steal money from banks
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and control economies.
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They could power off hospitals
or launch nukes,
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or they could just sit back
and watch all of us on our webcams
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without any of us knowing
that this is happening.
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Now, the fundamental unit of information
on all of the computers we're used to,
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like this one,
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it's called a "bit."
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A single bit can be one of two states:
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it can be a zero or it can be a one.
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When I FaceTime my mum
from the other side of the world --
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and she's going to kill
me for having this slide --
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(Laughter)
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we're actually just sending each other
long sequences of zeroes and ones
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that bounce from computer to computer,
from satellite to satellite,
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transmitting our data at a rapid pace.
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Bits are certainly very useful.
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In fact, anything
we currently do with technology
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is indebted to the usefulness of bits.
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But we're starting to realize
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that bits are really poor at simulating
complex molecules and particles.
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And this is because, in some sense,
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subatomic processes can be doing
two or more opposing things
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at the same time
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as they follow these bizarre rules
of quantum mechanics.
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So, late last century,
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some really brainy physicists
had this ingenious idea:
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to instead build computers
that are founded
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on the principles of quantum mechanics.
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Now, the fundamental unit of information
of a quantum computer,
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it's called a "qubit."
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It stands for "quantum bit."
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Instead of having just two states,
like zero or one,
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a qubit can be an infinite
number of states.
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And this corresponds to it being
some combination of both zero and one
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at the same time,
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a phenomenon that we call "superposition."
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And when we have two qubits
in superposition,
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we're actually working across
all four combinations
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of zero-zero, zero-one,
one-zero and one-one.
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With three qubits,
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we're working in superposition
across eight combinations,
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and so on.
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Each time we add a single qubit,
we double the number of combinations
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that we can work with in superposition
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at the same time.
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And so when we scale up
to work with many qubits,
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we can work with an exponential
number of combinations
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at the same time.
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And this just hints at where the power
of quantum computing is coming from.
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Now, in modern encryption,
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our secret keys, like the two factors
of that larger number,
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they're just long sequences
of zeroes and ones.
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To find them,
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a classical computer must go through
every single combination,
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one after the other,
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until it finds the one that works
and breaks our encryption.
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But on a quantum computer,
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with enough qubits in superposition,
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information can be extracted
from all combinations at the same time.
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In very few steps,
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a quantum computer can brush aside
all of the incorrect combinations,
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home in on the correct one,
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and then unlock our treasured secrets.
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Now, at the crazy quantum level,
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something truly incredible
is happening here.
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The conventional wisdom
held by many leading physicists --
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and you've got to stay
with me on this one --
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is that each combination is actually
examined by its very own quantum computer
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inside its very own parallel universe.
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Each of these combinations,
they add up like waves in a pool of water.
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The combinations that are wrong,
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they cancel each other out,
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and the combinations that are right,
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they reinforce and amplify each other.
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So at the end of the quantum
computing program,
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all that's left is the correct answer,
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that we can then observe
here in this universe.
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Now, if that doesn't make
complete sense to you, don't stress.
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(Laughter)
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You're in good company.
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Niels Bohr, one of
the pioneers of this field,
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he once said that anyone
who could contemplate quantum mechanics
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without being profoundly shocked,
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they haven't understood it.
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(Laughter)
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But you get an idea
of what we're up against,
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and why it's now up to us cryptographers
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to really step it up.
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And we have to do it fast,
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because quantum computers,
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they already exist in labs
all over the world.
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Fortunately, at this minute,
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they only exist
at a relatively small scale,
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still too small to break
our much larger cryptographic keys.
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But we might not be safe for long.
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Some folks believe that secret
government agencies
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have already built a big enough one,
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and they just haven't told anyone yet.
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Some punters say
they're more like 10 years off.
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Some people say it's more like 30.
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You might think that
if quantum computers are 10 years away,
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surely, that's enough time
for us cryptographers to figure it out
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and to secure the internet in time.
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But unfortunately, it's not that easy.
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Even if we ignore
the many years that it takes
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to standardize and deploy and then
roll out new encryption technology,
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in some ways, we may already be too late.
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Smart digital criminals
and government agencies
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may already be storing
our most sensitive encrypted data
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in anticipation for
the quantum future ahead.
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The messages of foreign leaders,
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of war generals
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or of individuals who question power,
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they're encrypted for now.
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But as soon as the day comes
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that someone gets their hands
on a quantum computer,
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they can retroactively break
anything from the past.
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In certain government
and financial sectors
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or in military organizations,
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sensitive data has got to remain
classified for 25 years.
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So if a quantum computer
really will exist in 10 years,
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then these guys are already
15 years too late
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to quantum-proof their encryption.
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So while many scientists around the world
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are racing to try to build
a quantum computer,
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us cryptographers are urgently
looking to reinvent encryption
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to protect us long before that day comes.
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We're looking for new,
hard mathematical problems.
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We're looking for problems that,
just like factorization,
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can be used on our smartphones
and on our laptops today.
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But unlike factorization,
we need these problems to be so hard
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that they're even unbreakable
with a quantum computer.
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In recent years, we've been digging around
a much wider realm of mathematics
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to look for such problems.
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We've been looking at numbers and objects
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that are far more exotic
and far more abstract
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than the ones that you and I are used to,
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like the ones on our calculators.
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And we believe we've found
some geometric problems
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that just might do the trick.
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Now, unlike those two-
and three-dimensional geometric problems
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that we used to have to try to solve
with pen and graph paper in high school,
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most of these problems are defined
in well over 500 dimensions.
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So not only are they a little hard
to depict and solve on graph paper,
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but we believe they're even
out of the reach of a quantum computer.
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So though it's early days,
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it's here that we are putting our hope
as we try to secure our digital world
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moving into its quantum future.
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Just like all of the other scientists,
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we cryptographers are tremendously excited
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at the potential of living in a world
alongside quantum computers.
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They could be such a force for good.
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But no matter what
technological future we live in,
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our secrets will always be
a part of our humanity.
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And that is worth protecting.
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Thanks.
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(Applause)